Particle detectors have been used for a variety of purposes to detect the presence and/or size of particles in various gases, including air. They have proved particularly useful to control contamination during precision manufacturing operations and are finding increasing use for determining the purity level of various liquids such as water. Determining the purity of liquids has become increasingly important in the semiconductor industry, because many of the fabrication processes use liquids. Any particulates contained in the liquids could contaminate the semiconductor products, thus reducing manufacturing yields.
Moreover, the present generation of microcomputers necessitates fabrication of electronics with components of ever decreasing sizes, making such components extremely susceptible to contamination of decreasing size. This has pushed the semiconductor industry to promulgate much higher quality filtration standards for particle detectors to sense particulate matter. Instrumental to achieving these higher standards is increasing the accuracy of the particle detectors by preventing the detection of bodies in the liquid which have a negligible effect on semiconductor manufacturing processes. One such body is gas present in the liquid.
Detecting gas bubbles in liquid can provide a false indication of the presence of particulate matter in the liquid. This can greatly increase the cost of manufacture of semiconductor products. A liquid might incorrectly be determined to be unsuitable for a manufacturing step, resulting in premature disposal and/or replacement. Therefore, it would be advantageous to remove bubbles from liquids which are being examined for the presence of particulate matter. Many prior art attempts have been made to separate bubbles from liquids.
U.S. Pat. No. 5,422,003 discloses a gas/liquid separation flow regulator which carries out gas/liquid separation by preventing an uncontrolled flow of sewage and facilitates control of liquid flow. The outer shell of the gas/liquid separation flow rate regulator is cylindrical in shape with its inner periphery providing a cylindrical surface. An edge inclining unidirectionally from one end to the other is formed at the upper edge of a partition plate for dividing the cylindrical shell into two chambers. The lower end of this inclined edge is butted to the cylindrical surface of the cylindrical member so as to form an overflow weir. A return port is centrally located on the cylindrical member and is disposed on the opposite side of the surface of the cylindrical member facing the overflow weir.
U.S. Pat. No. 5,338,341 discloses a separator for removing gases from water. An elongated tube having a cylindrical wall houses a concentric separator tube of a smaller diameter, leaving a vortex region between them. Water containing gas is tangentially injected into the vortex region, flowing downwardly to an exit port. In this manner, a vortex is formed within the separator which allows gases to collect at the top and be released by a valve.
U.S. Pat. No. 5,332,100 discloses a flotation method for separating mineral ores in a slurry. The slurry is introduced under pressure into the top of a first column through a downwardly facing nozzle, and gas is entrained into the slurry forming a downwardly moving foam bed in the first column. The foam bed passes from the bottom of the first column into a second column concentrically disposed about the first column. The gas and liquid separate in the second column, with the gas carrying particles upwardly, over a weir. The liquid/gas interface level in the second column is kept above the bottom of the first column, and an air flow rate into the top of the first column is controlled to keep the first column substantially full of foam.
U.S. Pat. No. 5,123,938 discloses a device for separating air from water and discharging the separated air. The device includes a housing with a feed aperture and a discharge aperture for the liquid to be degassed. The internal space of the housing is at least partially filled with open filling elements which have a large surface area relative to the used volume. The air present in water adheres to the surface of the filling element and forms little bubbles. The small bubbles increase into larger bubbles by coalescence, until they have sufficient floating power to break away from the filling element and rise to the surface of the water. The air is subsequently released through a valve in the top of the device.
U.S. Pat. Nos. 4,585,465 and 4,643,746 each discloses a method and device for causing bubbles in a fluid to coalesce into a coherent mass. The device discloses a cylindrical chamber having an input to allow fluid to tangentially enter the chamber. Fluid entering the chamber creates a vortex which flows from one end of the chamber to the other.
U.S. Pat. No. 4,102,655 discloses a bubble trap for removing bubbles from liquids, such as blood. The bubble trap includes a closed container for holding liquid, an inlet extending through the container bottom upwardly within the container to an inlet opening space below the container top. The container has a larger cross-sectional area than the inlet itself. An outlet extends through the container top downwardly within the container to an outlet opening, with the outlet opening being lower in the container than the inlet opening. Liquid flowing upwardly through the inlet opening into the container subsequently flows downwardly to reach the outlet opening. In this fashion, gas bubbles present in the liquid entering the inlet are allowed to rise above the surface of the liquid in the container, before passing through the outlet opening.
A drawback with the aforementioned devices is that the initial particle distribution in the liquid is disrupted to remove bubbles therefrom.
It is an object of the present invention, therefore, to provide an improved particle sensor having a device for removing bubbles from the stream of liquid entering the particle sensor while maintaining the original particle distribution in the liquid flow.
It is another object of the present invention to maintain a constant flow rate through a particle sensor while removing bubbles from liquid entering therein.